Recent developments in the application of live feeds in the freshwater ornamental fish culture

摘要

The industrial development of freshwater ornamental fish culture has been hampered by the lack of suitable live feeds for feeding the fish at the various production stages. This paper reports the recent developments in the applications of the freshwater rotifers (Brachionus calyciflorus), Artemia nauplii, decapsulated Artemia cysts and on-grown Artemia in the freshwater ornamental fish culture. Results demonstrate that the rotifers are an ideal starter feed for dwarf gourami (Colisa lalia), a typical freshwater ornamental fish species with larvae that are too small to ingest Artemia nauplii or Moina at its first feeding. Compared with the conventional yolk food, the use of rotifers as a starter feed significantly improves the growth and survival of the gourami larvae (Days 2-12), and the beneficial effects are extended to the subsequent Artemia-feeding phase (Days 13-32). The freshwater rotifers and Artemia nauplii are also useful in raising Discus larvae in the absence of their parents, which would eliminate the risk of larvae being eaten by the parent fish. Work on decapsulated Artemia cysts indicates that the cysts could be used as a substitute for Artemia nauplii or Moina in freshwater ornamental fish culture. The fry of all the five common ornamental fish species tested (guppy Poecilia reticulata, molly Poecilia sphenops, platy Xiphophorus maculatus, swordtail Xiphophorus helleri and neon tetra Hyphessobrycon herbertaxelrodi) could readily feed on the decapsulated cysts, and their performances in terms of stress resistance, growth and survival are comparable to or better than those fed on Artemia nauplii or Moina. A culture system for production of on-grown Artemia has also been developed specifically for the use in freshwater ornamental fish farms. The system, using diluted artificial seawater of 20parts per thousand for culture, has a mean production rate of 3 kg/m(3) of water in a 12-day cycle and a production capacity of 8 metric tons of on-grown Artemia a year. With the system, farmers could produce any specific size of on-gown Artemia of up to 5 mm to suit the age and size of their fish, by varying the time of harvesting. This characteristic, coupled with the use of bioencapsulation technique to enhance the quality of the on-grown Artemia, would make the organism an ideal nursery diet for freshwater ornamental fish. All these results show that the live feeds used in marine foodfish hatchery could be applied to freshwater ornamental fish culture to improve their performance.